Pressure relief valves are usually characterised as having a valve face with some form of seal pressed against it. The force to hold the pressure relief valve closed against pressure is supplied by a spring. The setting of the pressure relief is achieved by compressing the spring to varying degrees using a threaded adjuster. As the inlet pressure increases to the relief setting, the force generated by the inlet pressure exceeds the load supplied by the spring. This allows the seal to be lifted off the valve seat and the excess pressure is relieved.
As this type of relief valve must use such a spring to they require significant space to accommodate them. Springs and associated parts of such pressure relief valves represent several components to manufacture which can be expensive to manufacture and sell.
With valves or water supplies in general a problem can arise should there be abnormal excessive pressure build-up within the valve. For example, where a metal water pipe is connected to the inlet of a valve and the pipe is exposed to heat, such as sunlight, water in the pipe will expand and may create excessive closure pressure within a back-pressure chamber of a valve.
Excessive pressure can also arise within a valve chamber(s) owing to water passage blockage or dynamic components seizing. This can lead to fracture or similar malfunction of one or more of the components of a valve.
Also many such valves include traditional O-ring seals to seal junctions between two other components of the valve. As shown in FIGS. 7 and 8, O-rings are traditionally only used to seal by deforming under pressure. In a normal O ring, application as the pressure behind the O ring increases, the O ring is deformed further and a better seal is created.
In this specification unless the contrary is expressly stated, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date, publicly available, known to the public, part of common general knowledge; or known to be relevant to an attempt to solve any problem with which this specification is concerned.